1. Field of the Invention
The present invention relates to a manufacturing method of a plugged honeycomb structure which can preferably be used in a filter such as a diesel particulate filter and in which predetermined cells at an end surface of the structure are plugged.
2. Description of the Related Art
As a dust collecting filter typified by a diesel particulate filter (DPF), a filter having a honeycomb structure and made of a ceramic is used. Such a filter has a honeycomb structure having a large number of cells which are separated and formed by porous partition walls so as to constitute channels of a fluid, and each cell is plugged on one end portion opposite to that of an adjacent cell so that each end surface of the honeycomb structure has a checkered pattern.
When an exhaust gas including fine particles such as particulates is passed from one end surface of the filter (a plugged honeycomb structure), the exhaust gas flows into the structure from the cells having the end portions which are not plugged on the one end surface, passes through the porous partition walls and enters the other cells having end portions which are not plugged on the other end surface of the structure. Then, when the exhaust gas passes through the partition walls, the fine particles in the exhaust gas are trapped by the partition walls, and the cleaned exhaust gas from which the fine particles have been removed is discharged from the other end surface of the honeycomb structure.
Usually, to manufacture the plugged honeycomb structure having such a configuration, a method is employed in which as shown in FIG. 2, a mask film 4 to constitute a mask is attached to an end surface of a honeycomb substrate 1, holes 3 are provided at positions corresponding to opening end portions (cell opening end portions 7) of predetermined cells 2a and 2b of the mask film 4, and an end portion of the honeycomb substrate 1 is submerged into a container 5 in which a plugging slurry 6 is stored, whereby the plugging slurry 6 is allowed to permeate the predetermined cell opening end portions 7 through the holes 3 of the mask film 4 (e.g., see Patent Document 1).
In a case where the opening end portions of the predetermined cells are plugged by such a method, the slurry 6 for plugging does not sometimes permeate into a desired depth of the cells 2a and 2b. Moreover, the permeation depth of the plugging slurry in the cells 2a and 2b is not sometimes uniform, and there has been a problem that it is difficult to manufacture a homogeneous plugged honeycomb structure. In a case where the permeation depth of the plugging slurry which permeates the respective cells to be plugged is not uniform, fluctuations are generated in a pressure loss of each cell of the resultant plugged honeycomb structure, and a disadvantage that deviation is generated in a deposited amount of filtered matters or the like easily occurs.
As a concerned conventional technology for solving the above problems, a method is disclosed in which the plugging slurry having thixotropy is used, and the plugging slurry is allowed to permeate the predetermined cells of the honeycomb substrate while vibrated (e.g., see Patent Documents 2 and 3).
However, even in the methods disclosed in Patent Documents 2 and 3, there is a case where the plugging slurry 6 does not always permeate into the desired depth of the cells 2a and 2b, and the permeation depth is not uniform. Since a device for vibrating the plugging slurry is required, there is a tendency that manufacturing facilities to be used become huge and complicated.
[Patent Document 1] JP-A 2001-300922
[Patent Document 2] JP-A 6-190218
[Patent Document 3] JP-A 6-190224